Sorry, maybe I should ask more clearer. I've looked at dons article "Haskell as fast as C"[1], and tried to implement similar algorithm but for list of random numbers.
Please look at code: > import Text.Printf > import Control.Applicative > import System.Environment > import Data.Array.Vector > main = do > [size] <- map read <$> getArgs > let ints = enumFromToU 0 size :: UArr Int > printf "%d\n" (sumU ints) This code runs in constant space (on my pc ~25kb allocates on the heap) regardless of array size. So I tried to achieve similar with random list, just to replace `enumFromToU` with my own list generator. So the question - is it possible to implement random list similary to enumFromToU? [1]http://donsbot.wordpress.com/2008/06/04/haskell-as-fast-as-c-working-at-a-high-altitude-for-low-level-performance/ Thank you, Vasyl Pasternak 2010/2/9 Daniel Fischer <daniel.is.fisc...@web.de>: > Am Dienstag 09 Februar 2010 13:18:23 schrieb Vasyl Pasternak: >> Hello Cafe, >> >> I tried to generate memory-efficient list of random numbers, so I've >> used uvector library for this task. But it doesn't work, >> it still allocates more than 6Gb of memory for the random list of 10 >> >> million elements. Here is the code: > > Hmm, > > $ ghc -O2 --make ranVec > [1 of 1] Compiling Main ( ranVec.hs, ranVec.o ) > Linking ranVec ... > $ ./ranVec 10000000 +RTS -sstderr > 5130 > 4,919,912,080 bytes allocated in the heap > 883,256 bytes copied during GC > 26,896 bytes maximum residency (1 sample(s)) > 25,620 bytes maximum slop > 1 MB total memory in use (0 MB lost due to fragmentation) > > maximum residency is just eight bytes more than for 100,000 or 1,000,000 > numbers. I think that is constant space. > > The ~5 GB total allocation is sequential, ten million new StdGens are > produced and allocated, then immediately garbage collected. I see no > problem (except that StdGen is slow, e.g. the Mersenne twister is much > faster [and allocates less, but still linear in size]). > >> > import Text.Printf >> > import System.Random >> > import Control.Applicative >> > import System.Environment >> > import Data.Array.Vector >> > >> > randomListU :: (Int, Int) -> StdGen -> Int -> (UArr Int) >> > randomListU b g size = unfoldU size gen g >> > where gen g = let (x, g') = randomR b g >> > in JustS (x :*: g') >> > >> > main = do >> > [size] <- map read <$> getArgs >> > let ints = randomListU (-10, 10) (mkStdGen 1) size >> > printf "%d\n" (sumU ints) >> >> Could someone give a hint, how to implement this function in constant >> memory space? >> >> Thank you in advance. >> >> Best regards, >> Vasyl Pasternak > > _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
